Rising sea levels threaten shorebird habitats globally by trapping coastal wetlands against human-made barriers like dykes and roads. A first-of-its-kind systematic review published in Biodiversity and Conservation reveals that 89 per cent of examined studies found negative impacts on shorebird populations.
The Global Systematic Review on Shorebirds and Rising Seas
A newly published global systematic review in Biodiversity and Conservation examines how rising sea levels affect 29 species of shorebirds, including sandpipers, plovers, and oystercatchers. Researchers reviewed 37 studies containing data on rising sea levels and shorebirds. The findings point to predominantly negative outcomes for both habitats and bird populations.
Among the reviewed studies, 78 per cent identified negative impacts on habitat, while 89 per cent reported negative impacts on shorebird populations or individual birds. The research highlights a growing conservation challenge for coastal ecosystems worldwide.
Coastal Squeeze and Human Infrastructure
The review details a phenomenon known as coastal squeeze. As sea levels rise, coastal wetlands naturally need to migrate inland to survive. However, human infrastructure such as dykes, roads, and buildings often blocks that retreat.
In areas free of artificial barriers, wetlands can shift inland. Where coastal development or shoreline armouring is present, wetland habitat becomes trapped against a fixed boundary.
“As sea levels rise, coastal wetlands need space to retreat, but many of the places where shorebirds depend on these habitats are already constrained by dykes, roads and other development.”
Magel serves as the lead author of the review. Co-author Dr. Tara Martin, a professor in the Faculty of Forestry & Environmental Stewardship at the University of British Columbia, explained the mechanics of the squeeze.
Population Declines Beyond Simple Habitat Loss
The review indicates that the consequences for shorebirds extend beyond the physical reduction of space. In eight out of nine studies examining both habitat and population metrics, projected population declines were more severe than what would be predicted from habitat loss alone.
Shorebirds undertake migrations spanning hundreds to tens of thousands of kilometres. During these journeys, they rely on tidal flats and coastal wetlands as stopover sites to rest and feed.
In British Columbia, the Fraser River Estuary functions as a critical migration bottleneck. Large numbers of birds concentrate in this limited area along the Pacific Flyway to refuel.
Rising water levels shorten the daily window during which tidal flats remain exposed for feeding. At the same time, shifts in sediment composition, salinity, and water depth alter available prey. Higher water levels also elevate the risk of nest flooding for breeding birds.
“Shorebirds rely on these coastal habitats as places to rest and refuel during their migrations. If one of these important stopover sites is affected, it can have consequences for an entire population of birds because so many of them rely on these bottleneck sites.”
Timing and Nature-Based Coastal Adaptation
Although many studies evaluated projections extending toward the end of the century, the researchers emphasize that coastal adaptation decisions require immediate action. Planners face choices regarding how to manage coastal zones against encroaching tides.
- Protecting space directly inland from existing wetlands
- Removing or altering artificial barriers
- Enhancing sediment supplies to build wetland elevation
- Implementing managed coastal retreat where appropriate
As an example of testing elevation enhancement, the researchers point to the Sturgeon Bank Sediment Enhancement Pilot Project located in the Fraser River Estuary.
“The earlier we act and take these nature-based coastal adaptation approaches, the more space we will have for these wetlands to move and the more habitat we’ll save for the future.”
